The human immunodeficiency virus type 1 (HIV-1, also referred to as HTLV-III, LAV or HTLV-III/LAV) and, to a lesser extent, human immunodeficiency virus type 2 (HIV-2) is the etiological agent of the acquired immune deficiency syndrome (AIDS) and related disorders. Barre-Sinoussi, et al., Science, 220:868-871 (1983); Gallo, et al, Science, 224:500-503 (1984); Levy, et al, Science, 225:840-842 (1984); Popovic, et al., Science, 224:497-500 (1984); Sarngadharan, et al., Science, 224:506-508 (1984); Siegal, et al., N. Engl. J. Med., 305:1439-1444 (1981); Clavel., AIDS, 1:135-140 (1987). This disease is characterized by a long asymptomatic period followed by progressive degeneration of the immune system and the central nervous system. Studies of the virus indicate that replication is highly regulated, and both latent and lytic infection of the CD4 positive helper subset of T-lymphocytes occur in the tissue culture. Zagury, et al., Science, 231:850-853 (1986). The expression of the virus in infected patients also appears to be regulated as the titer of infectious virus remains low throughout the course of the disease. Both HIV-1 and 2 share a similar structural and functional genomic organization, having regulatory genes such as tat, rev, nef, in addition to structural genes such as env, gag and pol.
While AIDS, itself, does not necessarily cause death, in many individuals the immune system is so severely depressed that various other diseases (secondary infections or unusual tumors) such as herpes, cytomegalovirus, Kaposi's sarcoma and Epstein-Barr virus related lymphomas among others occur, which ultimately results in death. These secondary infections may be treated using other medications. However, such treatment can be adversely affected by the weakened immune system. Some humans infected with AIDS virus seem to live many years with little or no symptoms, but appear to have persistent infections. Another group of humans suffer mild immune system depression with various symptoms such as weight loss, malaise, fever and swollen lymph nodes. These syndromes have been called persistent generalized lymphadenopathy syndrome (PGL) and AIDS related complex (ARC) and may or may not develop into AIDS. In all cases, those infected with the HIV are believe to be persistently infective to others.
The activation of the latent HIV provirus from asymptomatic period has been reported to be governed by long terminal repeats (LTR) in the viral DNA. See Ranki, et al., Lancet ii:589-593 (1987); Fauci, et al., Science, 239:617-622 (1988); Zaguary, et al, Science, 231:850-853 (1985); Mosca, Nature (London), 325:67-70 (1987). The activity of HIV-1 is determined by the complex interaction of positive and negative transcriptional regulators that bind to specific sequences within the LTR. Cullen, et al., Cell, 58:423-426 (1989). Changes in the quantity or quality of these factors may underlie the activation of transcription of HIV-1 and HIV-2 latent provirus by a myriad of stimuli. See Fauci, Science, 239:617-622 (1988); Griffin, et al., Nature (London), 339:70-73 (1989); Nabel, et al., Science, 239:1299-1302 (1988). Specifically, phorbol 12-myristate-13-acetate (PMA) and Tumor Necrosis Factor-.alpha. (TNF.alpha.) are believed to be potent activators. In particular, TNF.alpha. is present in markedly enhanced levels in HIV infected individuals, suggesting that the cytokine plays an important role in the pathogenesis of AIDS. Lahdevirta, Am. J. Med., 85:289-291 (1988).
Most known methods for treating individuals infected with HIV have focused on preventing integration of the virus into the host cells' chromosome or on stages other than dealing with the provirus. Thus, one area of interest has been drugs that affect reverse transcriptase. Many of the proposed therapeutic methods, however, have not proven clinically effective. Indeed, even treatments that have resulted in clinical utility such as AZT (zidovudine) have not been reported to prevent the breakdown of the immune system in many patients after a number of years of treatment. Few methods have been reported to inhibit both expression of integrated provirus and chronic infection of HIV-1. Reverse transcriptase inhibitors, e.g., AZT, ddC, ddl have not been reported to have inhibitory effect on chronic infections.
Another method of treatment that has been proposed is to look for drugs that affect regulatory functions such as tat. The viral switch from latency to active replication requires regulatory protein including tat. The tat protein transactivates regulatory elements in the HIV-LTR and amplifies viral replication many thousand fold. Thus, it has been proposed that by inhibiting tat function, the virus will be stopped or greatly inhibited at the latent stage of viral infection with subsequent replication of the provirus substantially impeded. See, for example, Hsu, et al., U.S. Pat. No. 5,036,101, U.S. Pat. No. 5,041,438, Hsu, Science 254:1799-1800 (1992) and Hsu, et al., Proc. Natl. Acad. Sci. USA, 90:6395-6399 (1993). 7-chloro-5-(2-pyrryl)-3H-1,4-benzodiazepin-2(1H)-(one) (Ro 5-3335) was considered promising but animal studies revealed some toxicity for Ro 5-3335. An evaluation of 400 analogues resulted in finding 7-chloro-N-methyl-5-(1H-pyrrol-2-yl)-3H-1,4-benzodiaezepin-2 amine (Ro 24-7429) and in the clinical testing of Ro 24-7429. However, this clinical test was stopped.
Another series of compounds has been explored for treating individuals infected by HIV are xanthines. In particular, pentoxifylline (TRENTAL.RTM.), Hoechst-Roussel Pharmaceuticals, Inc. Pentoxifylline has been shown to decrease HIV-1 replication in acutely infected peripheral blood mononuclear cells (PBMCs) and in the Jurkat cell line [Fazley, et al., Blood 77:1653-1656 (1991)]. Clinical studies have begun with this drug. The present result of the preclinical and clinical study suggests that if there is a role for pentoxifylline in the treatment of AIDS, it will probably be as adjunctive therapy.
Thus, it would be desirable to have a new compound or a combination of compounds that can more effectively inhibit expression or replication of the HIV provirus in HIV infected cells and inhibit chronic infections then currently available. It would also be desirable to be able to effectively administer combinations of drugs at lower cumulative doses than possible currently. It would be particularly desirable to have a new therapy that can be used to treat already infected cells by means of inhibiting expression of provirus, or a means to keep the provirus dormant within infected cells.